In order for Lightspeed to facilitate shipping & coupon costs, you'll need to set up a "shipping" and "coupon" product. This article will go into greater detail about why this is, and what your options are for these products.
Shipping & Coupons
Lightspeed calculates shipping costs & coupons as separate line items on orders. To make this work, you'll have to create a "shipping" product and a "coupon" product. These products can be created as non-inventory items, and don't need to have a specific price. After they've been created Modern Retail will be able to access the product IDs, along with anything else we need.
If you have any further questions, please feel free to get in touch with your Project Manager using the messaging feature in the Onboarding Center.